iconGrid: Delay updating adjustment value on page switch

When switching to a newly created page, the adjustment's limits
haven't been adjusted yet. As a result, setting the new value
only works when the transition is animated.

To fix the non-animated case, use a MetaLater to set the adjustment
value.

https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/6315

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2670>

js/ui/iconGrid.js

@@ -1349,10 +1349,14 @@ var IconGrid = GObject.registerClass({
         if (!this.mapped)
             animate = false;
 
+        global.compositor.get_laters().add(
+            Meta.LaterType.BEFORE_REDRAW, () => {
                 adjustment.ease(newValue, {
                     mode: Clutter.AnimationMode.EASE_OUT_CUBIC,
                     duration: animate ? PAGE_SWITCH_TIME : 0,
                 });
+                return GLib.SOURCE_REMOVE;
+            });
     }
 
     /**